Telephone system



March 24, 1942. c. R. GRAY TEI/JEPHONE SYSTEM' Filed oct. 16, 1940vPatented Mar. 24, 1942 TELEBHONE SYSTEM Cecil R. Gray, Morristown, N.J., assigner to Bell Telephone Laboratories,

Incorporated; Newy York, N'. Y., a corporationof New York ApplicationOctober 16, 1940, Serial.No-. 3(i-1,380

5 Claims. (Cl'. 179-18) This invention: relates'to; telephone systemsand particularly tosystems comprising impulse controlled switches for;establishing connections between calling and called lines.

ItV isf an objectk of' the invention to. provide a more reliable impulserepeating arrangement and; to,l otherwise improve the impulse repeatingarrangement in, branch omcef selector-repeaters.

The invention; is an improved: impulse repeatngarrangementl in a branch,ofce-selector-repeater. The impulses are received by an impulsereceiving relayI which directly repeatsv these impulses; to the selectorswitch` ofthe selector-repeater, orY to succeeding` Selectors in the'branch office, and cont-rolsga repeatingfrelay whichtransmitscorresponding*impulses-.over a trunk to the main cnice in two separateygrounded circuits, each comprising one; off the conductors of the trunk.The impulse receiving relay is adjusted for response@ to impulsesreceived from` calling lines; andthe impulse. repeating rela-y isadjusted and has its releasing; time. controlledto;` transmit impulseslofJ a character-which insures satisfactory operati-on ofV impulsereceiving means at the distant end; of; the; trunk, they requiredvcharacter being dependentI upon the resistance and capacity ofthetrunkz.

A feature ofthe invention. is; an impulse repeating arrangement of; theaiorementionedcharacterfin a branch oiceZ selector-repeater in whichclosure of thel impulse repeatingk circuits; over the conductors of atrunk to the', main o'iee and closure of the supervisory4 bridge acrossthe conoluctors of; the4 trunky are contrclled by a relay which isinitially operated upon seizure of the l,

selector-repeaterprior.- to they receipt of a nrst train of impulses andthereafterV operated, in respense, to the rst; impulse of. each;succeeding train of impulsesl The operationl of thisA relay immediatelyVupon seizure insures against? releasing ofthe relay during receipt' of.ythe -rst train ofA dialv impulses,` i

A further feature is-the: provision off an auX- iliary' relay' in a;branch; ofce; Selector-repeater of the-aforementioned characterforcontrolling the connection of dial tone to, the. calling line. Accordingto; this,` feature; one.: of thev conductors of a calling line. is;connected througha talking condenser to oneof thefconductors of a trunkto the main oilice'im-mediatelyupon seizure of the selector-repeater andselection of a, trunk to the main office, the connection between theother conductor of the calling linel and other talking condenser being;even, at, a contactl of the auxiliary relay so that; thisfcendensel:will not interferewith the transmission of dial tone to; the callinglline. When thev rst dial impulse-is received from a calling station,the; auxiliary relay operates, to terminatethe transmission of dial toneand to: connect the other conductor ofthe calling line through the othertalking condenser to the other conductor of the trunk, the-connection ofboth, of the talking condensers between the conductors ofthe callinglineL andthe conductors of the; tru-nk to ther main oiiice beingeffective to prevent bell tapping at the calling station during dialingiThe drawing which forms a part of this specication shows, schematically;a system and circuit arrangement ink which the invention and itsfeatures are embodied. The invention is not, however, limitedin-.itsapplication to the particular system shownV in the drawing butisgenerally applicable to impulse? controlled switching and signalingsystems.

The drawing, whichy consists of a single ligure,

represents a system comprising a branch office and a mainoce. The branchoffice is represented bysubscribers stationsA and B, lines Ll and L2',aliney finder LE, a selector-repeater SR, a. service codey selector SCS,and a connector BC; andthe main oice is representedk by anincomingselectorIS. I The subscribers stations are of the common battery-typeIand include dials/or other impulse senders for control-ling theautomatic switches through` which connections between calling and calledlines; are established. The line-finder switch LF, selector switch S;service code selector switch SCS; connector switch BC'and incomingselector switch ISareof the Well-known twomotion step-by-step type.Reference may be had to Automatic Telephony, second edition, bySmith-and Campbell, pages 53 `to 65, inclusive, for a description of thestructure ofsuch switches andv their operation whenr used asv selectorsand connectors. Reference may,I behad to'the'patent toyR, L. Stokely,1,799,654 of April 7, 1931, for a descriptionof the operationr of atwo-motion stepby-step finder. The line finder LF' is represented byaset of brushes and one set of terminals.; the connector BC isrepresented by-its. brushesv and one set of terminals;- the. selectorSCS. is represented by its, line and release. relays in. addition toits. brushes 6I, 62, 634 and, 64,k andv a single set of terminals; andtheA selector IS is represented by its. brushes, one set. of, terminalsand its. line relay. l

'I,he;`selector-repeater4 is represented the drawing by the brushes.6J., 62.. 6.3, and` 6,4. and

one set of terminals, the vertical stepping magnet 1I, release magnet13, the vertical off-normal springs 14 and the 11th rotary step springs16 of the selector S; by the brushes 91 and 38 of the trunk huntingswitch TS; and by a line relay 41, release relay 42, dial tone controlrelay 51, impulse repeating relay 45, repeating control relay 53,switching relay 40, supervisory relay 44, and the contacts of otherrelays which are included in the arrangement for repeating impulses,received by the line relay 41 from a connected calling subscribers line,over a trunk to the main oflice and to succeeding selector and connectorswitches in the branch oiice. Reference may be had to the copendingapplication of H. Hovland, Ser. No. 361,365, iiled on Oct. 16, 1940, fora complete disclosure of this selector-repeater together with variousmain and branch oilice trunking arrangements in which theselector-repeater may be used. The same reference characters are usedfor the various elements of the selector-repeater shown in the drawingof this .application as are used for the same elements in theaforementioned copending application of H. Hovland.

Assume now that a call is originated at station A and that the linefinder LF is operated to connect the calling line L| to theselector-repeater SR in usual manner. Upon connection of line Ll to theselector-repeater SR, line relay 41 is operated in a circuit which istraced from battery through the upper Winding of relay 41, upper backcontact of relay 44, a lower back contact of relay 4U, middle brush ofline nder LF, through line Ll and the station A, upper brush of linefinder LF, upper back contact of relay 4B, a lower back contact of relay44, lower winding of relay 41. back contact of the 11th rotary stepsprings 16, a back contact of relay 43, a back contact of relay 51, andthrough a winding of dial tone transformer 58 to ground. At its innerlower front contact, relay 41 closes a circuit for operating relay 42and a circuit for operating relay 53. Relay 42 connects ground toconductor 33 to hold the line finder LF. As described in theaforementioned copending application of H. Hovland, the trunk huntingswitch TS is operated to select an idle trunk to the main oiiice at thesame time that the line nder LF starts hunting for the calling line;and, when an idle trunk is selected, relay D is operated. When relayk 54operates, it closes a circuit for operating the repeating relay 45 and acircuit for energizing the upper polarizing winding of relay 44. Withrelays 53, 50 and 45 operated, battery is connected through resistor 54,inner lower front contact of relay 53, upper front contact of relay 45,brush 91, one conductor of the selected trunk T to the main oiice, andthrough the right winding of line relay 233 of selector IS to ground;and ground is connected through resistor 5|, front contacts of relays53, 45 and 50, brush 93, other conductor of trunk T, and through theleft winding of relay Zilli to battery. R'elay 250 is thereby operatedto prepare the selector IS for response to dial impulses. 1t is to benoted that the operation of relays 45 and 5U also connects theconductors of the trunk to the main oiiice to one side of the talkingcondensers 59 and 60, the other side oi' condenser El! being connectedto one of the conductors of the calling line; but the connection betweenthe other side of condenser 59 and the calling line is open at a contactof relay 51 to prevent interference with the transmission of dial toneto the calling station.

' rst impulse, magnet 1| releases.

When the calling subscriber dials the first digit of the number of xthecalled subscribers station with which connection is desired, line relay41 is alternately released and reoperated as many times as there areunits in the digit dialed. The release of relay 41, at the beginning ofthe rst dial impulse, closes circuits, including the lower front contactof relay 42 and back contacts of relays 49 and 43, for operating thevertical stepping magnet 1| and for operating relay 51. Relay 51 closesa locking circuit to conductor 33 before it opens its operating circuit,disconnects the dial tone transformer 58 from the calling line, andcloses the connection between the calling line and the talking condenser59. The connection of condensers 59 and 60 to the calling line duringthe repeating of dial impulses over trunk T is eiective to aid thetransmission of these impulses and is also effective to prevent belltapping at the calling station during dialing. When relay 41 reoperatesat the end of the The release and reoperation of relay 41 in response toeach succeeding impulse of the train causes a corresponding operationand release of the vertical stepping magnet 1|, the brushes beingthereby advanced to the level corresponding to the digit dialed. Thevertical off-normal springs 14 are actuated when the shaft moves out ofnormal position due to the rst operation of stepping magnet 1|, thewinding of relay 53 being thereby connected, through a back contact ofrelay 44, in parallel with the stepping magnet 1| and under the controlof the back contact of relay 41 instead of in parallel with relay 42 andunder the control of the front contact of relay 41. Being slow inreleasing, relay 53 remains operated until after relay 41 reoperates atthe end of the last impulse. Relay 42 is also slow in releasing andremains operated during dialing. The release of relay 41 in response toeach dial impulse opens the operating circuit of repeating relay 45, therelease of relay 45 being delayed for a desired interval of time by thecharging of condenser 4B. When relay 41 reoperates at the end of eachimpulse, relay 45 reoperates.

The release and reoperation of relay 45, in response to each impulse,opens and closes the two ground return circuits over the conductors oftrunk T to cause a corresponding release and reoperation of the linerelay 20|), the brushes of selector IS being thereby advanced to a levelcorresponding to the digit dialed.

The selector-repeater SR. is arranged to absorb one or more digits byreturn of the brushes of selector S to normal after advance to a levelcorresponding to the digit to be absorbed, to release the trunk to themain ofce on calls to subscribers in the branch office, and to trunkhunt in a selected level either after the trunk to the main office hasbeen released or prior to the dialing of enough digits to determinewhether the called line is in the main office or in the branch office.The operation of the selector-repeater SR on various types of call andin various trunking arrangements is set forth in detail in theaforementioned copending application of H. Hovland.

If the rst digit dialed indicates that the call is for a subscriber inthe main oiiice or is one which must be completed through the main oice,th'e brushes of selector S are held opposite the selected level withouttrunk hunting, the impulses created by the dialing of the remainingdigits of the called number being repeated by relays 41 and 45 over thetrunk to the main oice to .contr'ol; theswitches throughwhichnthezdesired connection isF completed: in this:X case; relayfiil`is operated to open theY short' circuit. around resistor 31 to preventthe further operationv of vertical stepping magnet 1I in= response to.xdial impulses.

If' the first. digiti does. notA determine that the call is to becompleted over-the selected' trunk to the main. oice, the-digit' isabsorbed'by a return of.- the brushesI of' selector S to normal. Thebrushes are-'then advanced by the impulses created' by` the dialingA ofthe second digitl tov aV corresponding level; and these impulses arerepeated' by relay 45, in the manner hereinbefore described', over thetrunkv to the mainv oce. Iithev secondi digit indicatesthaty the'` call'is for a subscriberl in the mainl oiiice, relay 431 is op'- era-ted, theselector S is notl released, and: succeeding" trains of impulses arereptated to the main office without further operation of; the verticalstepping magnet 1 I.

If the second digit indicates that the called line is in the branchoiice, relay 48 is operated to release the trunk to the mainl oice.Trunk hunting may occur in the level corresponding to the second digitor ina levelI selected inf response to thev impulses for a succeedingdigit. When an idle trunk is found relays Il!)`v and 4U are operated, asdescribed in they copending-Y application of H. Hovland. Theoperation'of relay 4l.' causes the release of relays 41 andV 45, andconnects` the call-'ingA line through brushes 6| and 62y to the nextswitch in thev branch cnice;

K and the impulses created by the dialing of the remaining digits of thecalled subscribers num- I- ber control the switches in the branch olicethrough which connection with the called line is established.

If the second digit'does notV finallyv determine whether the call is amainl ora branch oiiice call, the brushes of selector S may or may notbe restored to normal to absorb this digit, depending upon theparticular trunking arrangement and the value of the digit. If thesecond digit is absorbed, the third digit may indicate that the call isa main office call; in which case relay 43 is operated and impulsescreated by further dialing are repeated over the trunk to the main omce.But if the second digit is not absorbed, the brushes of selector S areadvanced .f

additional digits are required to indicate whether th'e call is a mainor a branch office call, the impulses created by the dialing of thethird digit are repeated by relay 45 over the trunk to the main officein the manner hereinbefore described; and these impulses are alsorepeated by relay 41 over the trunk engaged by the brushes of selectorS. This trunk may be connected to a service code selector, other branchofce selector, or to a connector. In the drawing, the bank of selector Sis represented by two sets of terminals, one set connected to a servicecode selector SCS and the other connected to a connector BC. Assumingthe selection of a trunk leading to a service code selector SCS, thecircuit for repeating the third train of impulses includes the windingsof -line relay IUI, brushes 6| and 62, and front contacts of relay 41and 49. If the third or a succeeding train of impulses finally indicatesthat the call is to be completed in the branch oince, relay 40 isoperated in the manner Cil described; vinl the. copendngv application ofH. Hovlanda to.4 connect, the; callingV line directlyv totheibrushes;6I; and 62:.,l If, however, the thirdor a succeeding train. ofVimpulses: iinally determine that thecall is to be completed overv thetrunk tov themainy ofhce, relay 43t isoperated andl relay 49.- isyreleased', therebyv causing the release of the selector SCS; and, ifyadditional digits are dialed, the; impulses are repeated onlyV over thetrunk to the-main oiiic'e.. f

Ona call completed by switchesrin the branch oiice, the connection isheld under control of the calling subscriber by ground potentialconnected tothe terminal engaged by test brush 63. The disconnection ofthis holdingspotential when the conversation is ended causes the releaseof relay 4t andthe return of the selector S and line finder- LF tonormal in thef manner described' inthe copendi-ngapplicationI of H.'Hovland. On a call completed over a trunk to the main oilice relays 41,45 and' 42r are held under control of they calling subscriber, theitalking condensers 59 and G being included in the talking connectionbetween the calling line and the trunk to the main cnice. Whenr thecalling subscriber restores the station to normali,` relays 41, 45'?and' 412 re-V lease succession. eiectii-lg'the return of the. selectorrepeater SR and' line finder LF to normal? and' opening vthe bridgeacross the trunk tothe main oli-ice to effect the return ofv theswitches in the main oice to normal. y

It isparticularly` to be noted that the provision of a separaterepeating relay 45 for repeating impulses to the main ofli'ce permitsthe adjustment'of` this relay according to the length and'` characterofthe` outgoing trunks without affecting the response of the impulsereceiving relay- 41 toy dial; impuls-es from the calling line.

What is claimediis:

1. In combination, a line, an impulse receiv.- ing relay connected' to"said lineand responsive to current impulses therein, a trunk line, meanscomprising said impulse receiving relay and an impulse repeating relayfor controlling an imi. pulse repeating circuit over the trunk line, the

repeating relay being adjusted according to the resistance and capacityof the trunk line, an operating circuit for the repeating relaycontrolled by the impulse receiving relay, and a condenser connected tothe Winding of the repeating relay so as to render said relay slow inreleasing and thereby increase the length of each closure of the impulserepeating circuit during the repeating of impulses.

2. In combination, a line, an impulse receiving relay yconnected to saidline and responsive'to current impulses therein, a trunk line, impulsereceiving means connected t0 said line, means comprising said impulsereceiving relay and an impulse repeating relay for repeating impulses insaid line to said trunk line, each` of the conductors of the trunk linebeing included in a separate circuit for repeating the impulses t0 saidimpulse receiving means, the repeating relay being adjusted according tothe resistance and capacity of the trunk line, an operating circuit forthe repeating relay controlled by the impulse receiving relay, and acondenser connected to the winding of the repeating relay so as torender said relay slow in releasing and thereby increase the length ofeach closure of the impulse repeating circuit during the repeating ofimpulses.

3. In combination, a rst line, an impulse receiving relay connectedthereto, a circuit including said line for operating said relay, a tonesource included in said circuit, means for transmitting impulses in saidcircuit to said relay, a second line, means comprising saidV relay forrepeating impulses from said first line to said second line, anauxiliary relay, a circuit for operating said auxiliary relay closed inresponse to the rst impulse received by said impulse receiving relay,circuit means for maintaining the operation of said auxiliary relay, acondenser, and contacts actuated by the operation of said auxiliaryrelay for removing said tone source from the operating circuit of theimpulse receiving relay and for closing a talking connection includingsaid condenser between said first and second lines.

4. In a branch oice selector-repeater comprising an impulse controlledgroup selector and a non-numerical trunk hunting switch, a line relay,an impulse repeating relay controlled by said line relay to repeatimpulses in a separate grounded circuit over each conductor of a trunkselected by said non-numerical switch, a supervisory relay forconnection across the conductors of a selected trunk, a slow-to-releaserelay having normally open contacts in said impulse repeating circuitsand normally closed contacts in the connection between said supervisoryrelay and said conductors, means comprising a front contact of said linerelay for operating said slowto-release relay prior to the receipt ofdial impulses to prepare said impulse repeating circuits, meansincluding a contact of said line relay for operating the group selectorto select a group of terminals corresponding to a train of impulsesincoming to said line relay, means including contacts actuatedupon'movement of said selector out of normal position to transfer thecontrol of said slow-to-release relay from the front contact to a backContact of said line relay, whereby said slow-to-release relay is heldoperated until all of the impulses in the first' train incoming to saidline relay have been received and is reoperated upon release of saidline relay in response to the iirst impulse of each succeeding train ofimpulses.

5. In a branch oice selector-repeater comprising an impulse controlledgroup selector and a non-numerical trunk hunting switch, a line relay,an impulse repeating relay controlled by said line relay to repeatimpulses in a separate grounded circuit over each conductor of a trunkselected by said non-numerical switch, a supervisory relay forconnection across the conductors of a trunk selected by saidnon-numerical switch, a slow-to-release relay having normallyopencontacts in said impulse repeating circuits and normally closed contactsin the connection between said supervisory relay and said trunkconductors, means comprising a front contact of said line relay foroperating said slow-to-release relay prior to the receipt of dialimpulses to prepare said impulse repeating circuits, means including acontact of said line relay for operating said group selector to select agroup of terminals corresponding to a train 0fV impulses incoming tosaid line relay and to select a set of terminals therein connected to anidle trunk, means comprising a contact of said line relay for repeatinga train of impulses incoming to said relay after selection of an idletrunk by said group selector to said trunk, means including contactsactuated upon movement of said selector out of normal position totransfer the control of said slow-torelease relay from the front contactto a back contact of said line relay, whereby said slow-torelease relayis held operated until all of the impulses in a rst train incoming tosaid line relay have been received and is reoperated upon release ofsaid line relay in response to the rst impulse of each succeeding trainof impulses.

CECIL R. GRAY.

